Intradermal injections are used for delivering a variety of substances. Many of these substances have proven to be more effectively absorbed into or react with the immune response system of the body when injected intradermally. Recently, clinical trials have shown hepatitis B vaccines administered intradermally are more imunogenic than if administered intramuscularly. In addition, substances have been injected intradermally for diagnostic testing, such as, for example using what is known in the art as the “Mantoux test” to determine the immunity status of the animal against tuberculosis and the immediate hypersensitivity status of Type I allergic diseases. It is desirable, in some instances, to provide a prefilled container filled with one of these substances and to mate the needle cannula to the container just prior to administering the injection.
An intradermal injection is made by delivering the substance into the epidermis and upper layer of the dermis. Below the dermis layer is subcutaneous tissue (also sometimes referred to as the hypodermis layer) and muscle tissue, in that order. There is considerable variation in the skin thickness both between individuals and within the same individual at different sites of the body. Generally, the outer skin layer, epidermis, has a thickness between 500-200 microns, and the dermis, the inner and thicker layer of the skin, has a thickness between 1.5-3.5 mm. Therefore, a needle cannula that penetrates the skin deeper than about 3.0 mm has a potential of passing through the dermis layer of the skin and making the injection into the subcutaneous region, which may result in an insufficient immune response, especially where the substance to be delivered intradermally has not been indicated for subcutaneous injection. Also, the needle cannula may penetrate the skin at too shallow a depth to deliver the substance and result in what is commonly known in the art as “wet injection” because of reflux of the substance from the injection site.
Due to the inherent limitations of the standard needle assembly, the standard procedure for making an intradermal injection is known to be difficult to perform, and therefore dependent upon experience and technique. This procedure is recommended to be performed by stretching the skin, orienting the needle bevel to face upwardly, and inserting a 26 Gauge short bevel needle cannula to deliver a volume of 0.5 ml or less of the substance into the skin of an animal with the needle cannula being inserted into the skin at an angle varying from around 10-15 degrees to form a blister or wheal in which the substance is deposited or otherwise contained. Accordingly, the technique utilized to perform the standard intradermal injection is difficult and requires the attention of a trained nurse or medical doctor. Inserting the needle to a depth greater than about 3.0 mm typically results in a failed intradermal injection because the substance being expelled through the cannula will be injected into the subcutaneous tissue of the animal.
The most frequent cause of a failed intradermal injection is derived from inserting the needle into the skin at an angle greater than 15 degrees relative to the flattened skin surface. A further cause of error is derived from pinching rather than stretching the skin in the area of the injection, which is normally done when giving a subcutaneous rather than an intradermal injection. Pinching increases the likelihood of giving a subcutaneous injection. Procedural errors as described above result in delivering the contents of the injection into the subcutaneous layer, which can reduce the effectiveness of the injection, as well as possibly deliver the substance in a way not approved for delivery. Intradermal injections performed by using the standard procedure also are known to cause a significant amount of pain to the recipient of the injection because the needle cannula is inserted into the skin at an angle of about fifteen degrees. By inserting the needle cannula at this angle, about 5 mm to about 6 mm of the needle is actually inserted into the skin. This results in a significant disruption of the pain receptors dispersed throughout the upper layers of the skin. Also, self-administered intradermal injections are not possible using the present method.
Accordingly, there has been a long felt need for a needle assembly attachable to a prefillable container enabling a simplified method of performing an intradermal injection of substances which overcomes the problems and limitations associated with the use of conventional devices, especially reducing the probability of error and pain caused from the injection by making such injections less dependent upon experience and technique. In addition, there has been a need to reliably limit the depth of penetration of the needle cannula into the skin of the animal to avoid entry into the subcutaneous layer of the skin as well as reliably fix the orientation of the needle cannula relative to the skin. Also, there has been a need to apply pressure to the skin of the animal to facilitate formation of the blister or wheal in the skin in which the substance is deposited or otherwise contained and avoid wet injections. Further, pressure is applied to mask the pain derived from the intradermal injection by stimulating the muscle fibers to block the pain receptors. Still further, there has been a need to provide an needle assembly capable of addressing each of these shortcomings and yet be mated to the prefilled container just prior to administering the injection.